UPDATE
when i add a static route to my machine (172.20.0.179) to the 172.18.x.x network everything is working fine.
So i think it has something to do with our nokia checkpoint.
Something like asynchronous routing?
Because traffic flows from the 172.18.x.x directly into the 172.20.x.x network and from the 172.20.x.x network it goes first through a nokia checkpoint and then back to the pfsense firewall?
See my brilliant paint for more explanation ;D

